A vehicle is exposed to various accelerations and vibrations which are caused by the road conditions and the acceleration/deceleration of the vehicle, and such accelerations and vibrations may be directed in the fore-and-aft, vertical and lateral directions. When a vehicle operator is exposed to such an acceleration or vibration condition while stepping on an accelerator pedal, the foot of the vehicle operator placed on the accelerator pedal may apply an unintended force to the accelerator pedal owing to the shock of such accelerations and vibrations and/or the inertia force of the vehicle operator's foot applied to the accelerator pedal, and this may cause an inadvertent depressing or releasing of the accelerator pedal.
The movement of the accelerator pedal directly affects the drive force of the vehicle, and such an inadvertent fluctuation of the depression of the accelerator pedal owing to the accelerations and vibrations of the vehicle body is not desirable as it causes an unintended fore-and-aft acceleration or deceleration of the vehicle.
It has been proposed to detect or estimate an external force on an accelerator pedal caused by the vibrations of the vehicle, and control the reaction force of the accelerator pedal in dependence on the external force. See Japanese patent laid open publication No. 2006-117102 (patent document 1).
According to this prior art, the pedal reaction force is increased when the vehicle is vibrating so that the accelerator pedal is prevented from being depressed much further than the vehicle operator intends. However, this prior art requires a control mechanism for dynamically changing the reaction force of the accelerator pedal which is mechanically complex so that a large number of component parts are required and the manufacturing efficiency is reduced. Furthermore, if the vehicle operator tries to accelerate the vehicle when the vehicle is vibrating, the vehicle operator is required to depress the accelerator pedal more forcibly than usual, and this adds to the effort required for the vehicle operator to depress the accelerator pedal.